Reconstructing focused ion beam current density profile by iterative simulation methodology

Abstract

The authors present a simulation-based methodology for reconstructing the focused ion beam current density profile using sputtering and implantation information available from transmission electron microscopy images of single beam-width lines created using a Ga+ beam on SiO2 substrate. A bi-Gaussian distribution for the ion beam was assumed. Ga+ implantation in fused silica substrate was iteratively simulated sweeping through beams of varying parameters using srim monte carlo software. The resulting lateral distribution and density of the implanted Ga were visualized and compared to the experimental implanted Ga distribution on the cross-section of a physically sputtered line. Beam simulation parameters resulting in a close match between simulated and experimental Ga+ implantation were accepted as describing the primary ion beam. The authors apply the current density distribution of reconstructed beam profile to analyze single beam-width line profiles etched with XeF2 precursor and deposited with W(CO)6 precursor. Results indicate that XeF2 gas assisted etching and W(CO)6 deposition processes were enhanced in the peripheral regions of the Ga+ ion beam which are characterized by low current densities on the order of 1.0 ×10−4 pA/nm2. A similar simulation methodology as presented here can presumably be applied to reconstruct beam current density profiles and applied to characterize gas-assisted processes for arbitrary combinations of primary ion species and gaseous precursors with suitable substrates. This methodology is directly applicable to development of industrial processes using focused ion beams for modification of semiconductor, microelectromechanical systems, microfluidic, and photonics devices.